Inter Frequency Handover

Inter Frequency Handover

UMTS on 2nd Carrier

Inter-Frequency Handover • Inter-frequency handover (IFHO) allows the

UTRAN to switch the serving frequency of the UE during dedicated channel state.

• Like the inter-RAT handover, the inter-frequency handover procedure consists of two steps: – The inter-frequency measurements

– The inter-frequency handover

• Since IFHO is a hard handover, it employs compressed mode to facilitate inter-frequency measurements.

Enabling IFHO

Parameter Level at&t Default Comment

fddIfHoSupp RNC FALSE *

Indicates if the RNC supports Inter-Frequency Handover.

* Should be set to TRUE to enable IFHO.

defaultHoType RNC 1 *

For performing IFHO or IRAT HO for UEs that have drifted to

another RNC, the SRNC needs to know the handover type for cells

in the DRNC. This information is set in defaultHoType in the

WcdmaCarrier MO and is defined for each carrier that serves as a

DRNC. IFHO_PREFERRED = 0, GSM_PREFERRED = 1

NONE = 2 *Should be set to 0 to allow IFHO in the drift RNC.

RNC


hoType Cell 1 *

This parameter indicates per cell if GSM HO, IFHO or none shall

be attempted: IFHO_PREFERRED = 0, GSM_PREFERRED = 1

NONE = 2 * Should be set to 0 to enable IFHO.

Cell


C_IfHoAllowed UeRc 0 *

Indicates per UeRc state if Inter-Frequency HO is allowed;

0 = Not Allowed, 1 = Allowed * Should be set to 1 to enable IFHO

C_gsmHoAllowed UeRc 1

Indicates per UeRc state if Inter-RAT HO is allowed;

0 = Not Allowed, 1 = Allowed

UeRc

IFHO Block Diagram

Call Start: DCH ESTABLISHED AND UE CAPABILITIES CHECK

IF neighbours exist AND

hoType condition fullfilled AND

IFHO allowed for current UeRc

IF EVALUATION STOP

GOOD QUALITY DETECTED (event 2f or 6b)

IF EVALUATION START (Compressed Mode)

CONNECTION QUALITY MONITORING START

BAD QUALITY DETECTED (event 2d or 6d)

IFHO CONDITIONS FULLFILLED (event 2b)

IFHO EXECUTION

2

3

4

5

6

4a

This part is common to IF and IRAT

UE moves to new carrier

IF neighbours not available OR

IFHO not allowed for current UeRc

yes

no

AS or RAB state change

yes

4b

1

Connection Quality Monitoring

uplink

Ue Tx Power

Ec/No RSCP UeTxPwr Configurable thresholds for DL based event triggering

CONNECTION QUALITY MONITORING

quality = good if all

measurement items are good

quality = bad if at least

one measurement is bad

bad bad bad good good good

downlink

CPICH RSCP CPICH Ec/No

2

Max UE Tx pwr for UL based event triggering

Connection Quality Monitoring consists of measurements based on: •DL P-CPICH Ec/No and DL P-CPICH RSCP measurements running in parallel; •UL UE Tx power measurements.

Bad Quality Detected

UE RNC

RRC Connection Request

RRC Connection Setup

RRC Connection Setup Complete

RRC Measurement Control

BAD QUALITY DETECTED (event 2d or 6d)

RRC Measurement Report

MEASUREMENT REPORT

Reporting event type

• Event 2d with indication if it is referring to

Ec/No or RSCP measurements

• Event 6d (UETX pwr)

E e2d Ec/No

E e2f Ec/No

R e2d RSCP

R

e2f RSCP

T

e6b

T e6d

Connection Quality Status Update Ec/No RSCP UeTx

3

Event 2d: If the WCDMA quality on the current used frequency goes below usedFreqThresh2d threshold minus the corresponding hysteresis, and the condition is maintained during timeToTrigger2d. (can be EcNo or RsCP) Event 6d: If the UE Tx Power reaches the maximum and the condition is maintained during a time period timeToTrigger6d

Event 2f: If the WCDMA RAN quality on the current used frequency goes above usedFreqRelThresh2f+usedFreqThresh2d threshold plus the corresponding hysteresis, and the condition is maintained during timeToTrigger2f. (can be EcNo or RsCP) Event 6b: If the UE Tx Power goes below ueTxPowerThresh6b threshold, and the condition is maintained during a time period timeToTrigg6b

OR OR

IFHO Evaluation Start Compress Mode 4

• Compressed Mode Methodology is dependant on the Bearer type:

– For conversational bearers, compressed mode is accomplished by accelerating the data transmission rate (by halving the spreading factor) for a brief period of time to allow a break in transmission for IFHO OR IRAT measurements

– For non-conversational class bearers, data transmission is briefly suspended by higher layers (layer2) to allow for IFHO or IRAT measurements to be performed

• Due to limitations in the Compressed Mode gap patterns used, measurements for Inter-Frequency Evaluation and Inter-RAT Evaluation are not performed simultaneously. A decision has to be made on whether evaluation should be made for Inter-Frequency handover or Inter-RAT handover or Inter-RAT Cell-Change.

• The type of handover to be attempted is set by the parameter hoType (IFHO_PREFERRED, GSM_PREFERRED, NONE) and per carrier frequency for external DRNC cells (defaultHoType).

IFHO Condition Fulfilled

IFHO CONDITIONS FULFILLED (event 2b)

RRC Connection Request

RRC Connection Setup

RRC Connection Setup Complete





UE RNC

time

Ec/No or RSCP

Used frequency Ec/No / RSCP

Non-used frequency

Execute handover

(event 2b) Start IF meas.

Condition on non-used frequency: • Ec/No > NonUsedFreqThresh4_2bEcno + Hyst4_2b / 2

AND • RSCP > NonUsedFreqThresh4_2bRscp + Hyst4_2b / 2

AND

•Depending on whether the IF measurements were started due to Ec/No or •RSCP or •UE Tx power

5

Condition on used frequency: • Ec/No < UsedFreqThresh2dEcno + UsedFreqRelThresh4_2bEcno - Hyst4_2b / 2

• RSCP < UsedFreqThresh2dRscp + UsedFreqRelThresh4_2bRscp - Hyst4_2b / 2 • RSCP < UsedFreqThresh2dRscp + UsedFreqRelThresh4_2bRscp + utranRelThreshRscp - Hyst4_2b / 2

• If the Inter-Frequency Handover Evaluation receives an event 2b MEASUREMENT REPORT while it is already processing another MEASUREMENT REPORT, the new one is buffered.

• There is one buffer for the only specified event 2 MEASUREMENT REPORT. The buffer holds only the last received report so a new received report overwrites a report already in the buffer.

• If no event 2b report is buffered, then IFHO attempts shall be repeated. The number of repeated attempts, not including the first attempt, is set by the parameter IfhoAmountPropRepeat.

• The time interval between the attempts is set by parameter IfhoPropRepeatInterval.

IFHO Condition Fulfilled 5

IFHO Execution Flow Diagram

IFHO EXECUTION

• The Execution part assesses the amount

of resources in the target WCDMA RAN

cell, according to the proposal received

from the Inter-Frequency Handover

Evaluation algorithm. It interacts with the

Capacity Management functions.

• If the attempt succeeds, the actions

necessary to fulfill the handover proposal

are executed.

• If execution fails, exception handling is

performed to return to stable situation and

keep the UE connection on the source

WCDMA RAN frequency.

6

IFHO – Parameters Parameter Level at&t Default Comment

usedFreqThresh2dEcNo Cell

-12 (HHO)

-15 (SHO)

Threshold for event 2d (the estimated quality of the currently used

WCDMA RAN frequency is below a certain threshold).

Used if measurement quantity is configured to be Ec/No.

usedFreqThresh2dRSCP Cell

-103 to -109 (HHO)

-112 (SHO)

Threshold for event 2d (the estimated power level of the currently used

WCDMA RAN frequency is below a certain threshold).

Used if measurement quantity is configured to be Rscp.

timeToTrigger2dEcNo RNC 320

Time in milliseconds (ms) between detection of event 2d and sending

of the measurement report, when the measurement quantity is CPICH

EC/NO.

timeToTrigger2dRSCP RNC 320

Time in milliseconds (ms) between detection of event 2d and sending


RSCP.

hysteresis2d RNC 4 Hysteresis for event 2d (Unit: 0.5 dB).

usedFreqRelThresh2fEcno RNC 2

Relative threshold for event 2f vs event 2d for the used frequency

when the measurement quantity is Ec/No.

usedFreqRelThresh2fRscp RNC 6

Relative threshold for event 2f vs event 2d for the used frequency

when the measurement quantity is RSCP.

timeToTrigger2fEcNo RNC 640

Time in milliseconds (ms) between detection of event 2f and sending


EC/NO.

timeToTrigger2fRSCP RNC 640

Time in milliseconds (ms) between detection of event 2f and sending


RSCP.

hysteresis2f RNC 2 Hysteresis for event2f (Unit: 05.dB).


ueTxPowerThresh6b RNC 21 Threshold for event 6b.

timeTrigg6b RNC 1280

Time between detection of event 6b and sending of the measurement

report.

timeTotrigger6d RNC

N/A

320 *

Time between detection of event 6d and sending of the measurement

report

* Default value by Ericsson – has replaced timeTrigg6a

usedFreqRelThresh4_2bEcNo RNC -1

Relative threshold for event 2b vs event 2d, when the 2d measurement

with measurement quantity CPICH EC/NO was started.

This parameter is used to compute the absolute 2b Ec/No used

frequency threshold, by adding it to the current 2d Ec/No threshold

(absolute 2b Ec/No used frequency threshold = usedFreqThresh2dEcno

+ usedFreqRelThresh4_2bEcno).

usedFreqRelThresh4_2bRSCP RNC -3

Relative threshold for event 2b vs event 2d when the 2d measurement

with measurement quantity CPICH RSCP was started.

This parameter is used to compute the absolute 2b Rscp threshold, by

adding it to the current 2d Rscp threshold (absolute 2b Rscp used

frequency threshold = usedFreqThresh2dRscp +

usedFreqRelThresh4_2bRscp).

nonUsedFreqThresh4_2bEcNo RNC -13

Threshold for measurement 4 event 2b for the non-used frequencies

when the measurement quantity is Ec/No.

nonUsedFreqThresh4_2bRSCP RNC -105

Threshold for measurement 4 event 2b for the non-used frequencies

when the measurement quantity is RSCP.

IFHO – Parameters


utranRelThreshRSCP RNC 5

Relative threshold used during bad connection quality, when the

measurement quantity is CPICH RSCP.

The absolute 2b used frequency threshold will be calculated as:

absolute 2b Rscp used frequency threshold = usedFreqThresh2dRscp +

usedFreqRelThresh4_2bRscp + utranRelThreshRscp.

timeTrigg4_2b RNC 100

Time between detection of event 2b and sending of the measurement

report, for measurement 4.

Unit: 1 ms

Hyst4_2b RNC 10

Hysteresis for measurement 4 event 2b.

Unit: 0.1dB

IfhoAmountPropRepeat RNC 4

Maximum number of repeated proposals of non-used frequency cell(s)

for handover based on the same measurement report

IfHoPropRepeatInterval RNC 5

Minimum time interval between proposals of the same non-used

frequency cell for handover based on the same measurement report.

Unit: 0.2 seconds

IFHO – Parameters

IFHO Scenario – Overlay

Adding the second carrier where capacity increase is most needed.

As the traffic in the network increases, the second carrier coverage is then expanded gradually.

Call continuity to support for

mobile units leaving and

entering the multi-carrier area

while in Cell_DCH stateis

usually provided through IFHO

UMTS F1

UMTS F2

UMTS F1

IFHO Scenario – Overlay

UMTS F2

F1 – IRAT and F2 - IFHO

Border setting for 2d

thresholds for EDGE f2 cells.

usedFreqThresh2dEcNo,

usedFreqThresh2dRSCP.

B

B

B

B B

B

B

B B

Ensure quality on non used freq

before event 2b.

nonUsedFreqThresh4_2bEcNo,

nonUsedFreqThresh4_2bRSCP

These thresholds should always

be higher than 2d triggers so

ping-pong hard handovers don’t

occuer.

F2

F1 IRAT IRAT IRAT IRAT IRAT

IFHO IFHO IFHO

GSM

Cell Reselection IFLS IFHO IRAT

IFHO Scenario – Infill sites

A F2 cell is added where there is a coverage hole.

Scenario is only caused when F1 cell cannot be built in the area.

Requires the spectrum to be cleared for both band!

Long term plan should be to either

convert the F2 cell into F1 or dual

banding the infill site

UMTS F1

UMTS F2

IFHO Scenario – Infill sites F1 – IRAT/IFHO and F2 -

IFHO F2

F1 IRAT IFHO IFHO IRAT

GSM

IFHO

UMTS F1

UMTS F2

2d thresholds for F2 are set

to border settings for quicker

IFHO

2d thresholds for F1 are set

to interior settings for slower

IFHO.

Highway

Small road

Cell Reselection IFHO IRAT

Drop Call! Due to limitations in the Compressed Mode gap patterns used, measurements for Inter-Frequency Evaluation and Inter-RAT Evaluation are not performed simultaneously. A decision has to be made on whether evaluation should be made for Inter-Frequency handover or Inter-RAT handover or Inter-RAT Cell-Change.

Documents

Inter Frequency Handover